Centrifugal pumps include canned-motor centrifugal pumps and magnetic-drive centrifugal pumps. Magnetic-drive pumps are generally well-suited for pumping caustic and hazardous fluids because shaft seals are not required. Instead of shaft seals, magnetic-drive pumps generally feature a pump shaft separated from a drive shaft by a containment shell. The drive shaft is arranged to rotate with a first magnetic assembly, which is magnetically coupled to a second magnetic assembly. The second magnetic assembly applies torque to the pump shaft to pump a fluid contained by the containment shell.
An operational range of a hydraulic thrust balancing system within a pump may be limited to a critical operating point of low head and high flow. At a lower head or higher flow than the critical operating point, an inadequate static pressure differential within the pump may prevent the hydraulic thrust balancing system from maintaining an axially balanced position of the impeller. Instead, an axial bearing about an eye of the impeller may absorb axial thrust where inadequate static pressure is present for reliable operation of the thrust balancing system. However, the axial bearing can require routine maintenance, can heat the pumped fluid, and can add drag to the drive motor of the pump. Thus, a need exists for a pump with an extended operational range, for a thrust balancing system, over a complete desired range of head and capacity.
When changes in inlet flow of the fluid disrupt the axial position of the impeller from an axially balanced position, a thrust balancing system may respond too slowly or with an inadequate restoring force to avoid frictional contact between the members of the axial bearing before the impeller returns to an axially balanced position. Thus, a need exists for a thrust balancing system that provides a greater stiffness or a more responsive restoring force to avoid stress and undesired wear to an axial bearing.